Q10 of 68 Page 30

Calculate the efficiency of packing in case of a metal crystal for

face-centred cubic (with the assumptions that atoms are touching each other).

Let the base of the hexagon is a and the height is c


Each angle in hexagonal will be 60 degree at the base


Packing efficiency of Hexagonal close- packed lattice



a = 2r c = 1.633a




= 74%


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Calculate the efficiency of packing in case of a metal crystal for

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Calculate the efficiency of packing in case of a metal crystal for

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Silver crystallises in fcc lattice. If edge length of the cell is 4.07 × 10–8 cm and density is 10.5 g cm–3, calculate the atomic mass of silver.

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A cubic solid is made of two elements P and Q. Atoms of Q are at the corners of the cube and P at the body-centre. What is the formula of the compound? What are the coordination numbers of P and Q?